Hey folks, some of you have been keeping up with my project, since i've put an opened up exhaust on my internally wastegated Greddy 18g kit.

Well, I have not completed testing of the porting job I did, but the early results are promising. The porting seems to be helping me control boost better, but it looks like it still creeps a bit..but i immediately get off the gas so i dont know if its a bump or a big climb...anyway

my timing map is a stock GSR map at 0psi and in vacuum. for my 0-10psi region, i have been retarding timing at around 2 degrees per psi. yes TWO degrees, so at 8psi i was only at about 15 degrees advance. I am thinking this is SEVERELY retarding the timing and might be contributing to my problems. and here is my theory

the significantly retarded timing, coupled with my safely rich a/f ratio (11.5:1) means that the air fuel mixture gases are still burning when the exhaust valves open. so the piston is pushing out hot gases that are still expanding. i think this is causing my exhaust manifold pressure to climb higher than normal, which makes the turbo spool more and the internal WG cant balance the pressure enough.

so if i use a more conservative timing retard rate, like 1degree per psi (or less??? ) i'll have less hot high pressure gases being pushed into the exhaust manifold, and the internal WG might work better, not to mention i'll have a pissload more power since i am not wasting all that energy anymore.

i dont need such an agressive retard rate anymore since i am watching the knock sensor closely for ping and there doesnt seem to be any hiccups leftover from the turbo install.

anyone have experience with this? i think this is another phenomenon that doesnt occur with "race" setups that have large external wastegate setups (tial 35mm). hopefully i will be able to do some testing to back up the theory later tonite.

 

Makes sense to me. It could not hurt to try and see what happens. as long as you are running a good a/f ratio and watching the knock sensor. 2 degrees of retard of timing is a lot. 1 degree does seem more conservative and may look like it will work.

 

just trying to convince myself more

falconGSR: everything else being equal ....when you retard your timing, you get less power
falconGSR: right?
falconGSR: so there is extra energy that you dont take advantage of (maybe you cant cause you'll ping)
falconGSR: but anywya
falconGSR: so that extra energy gets shoved out of the engine
falconGSR: as the a/f ratio is still burning releasing energy, but since you ignited it late, it doesnt make as much cylinder pressure, and then that energy gets pushed out the exhaust
falconGSR: problem is in my case, that extra energy is going into the exhayst manifold where my internal WG is
falconGSR: and its causing the pre-turbo pressure to spike, which causes the turbo to spool, if the internal WG cant relieve the pressure quick enough.
falconGSR: so all i have to do is advance my timing (making sure it doesnt detonate) and i will fix my boost creep problem
falconGSR: and have more power

 

Dude, you'd better advance your timing and get the hell out of Iraq!

 

i guess i'll ask the supra guys if they ever had issues with stock turbos and retarding timing

 

Here is a perfect solution to your problem ----> SELL YOUR GREDDY TURBO

Buy a Precision Turbo and Inline Pro Manifold.


Problem Solved.

 

i'm not giving up on this.

 

15 degrees at 8psi? Wow! And afr of 11.5:1? Double wow!

 

Dark: timing as retarded as yours might cause EGT to go up some
Dark: which will make turbo spool more
Dark: which MIGHT make boost spikes
falconGSR: thats the same idea i am trying to esplain
falconGSR: wow. damn good point
falconGSR: i didnt think of it in those terms!
Dark: lol... i see you had the same idea i had
Dark: but yeah
Dark: not just the "still expanding" gases
Dark: but to simplify it more
Dark: just think EGT
Dark: becuz EGT = turbo spins

*falcon smacks forehead*

i think i caused this problem.

 

thanks for not giving away my AIM name Falcon.

 

I've given you my input on the matter

 

problem fixed. details coming.

 

please keep us posted falcon

 

Brilliant Mr. Falcon! Simply Brilliant!

 

i learned an important lesson tonite.

whenever you have wasted energy left over from the combustion process, that energy gets piped out of the combustion chamber and into the turbo manifold, where it will try to raise the manifold pressure and spool the turbo.

the rule is, whenever you retard your timing or add excess fuel, your exhaust manifold pressure will go up and your turbo will spool more . this is a good thing when you're trying to spool the turbo as you enter boost, but retarding the timing OR dumping fuel suddenly while at full boost will cause your boost to spike. if your wastegate can handle the new pressure, the spike will go down and you'll never know what happened. if it overwhelms the WG, like it did in my case, then the boost level will climb and run away, and as more exhaust gases enter the turbo manifold, more pressure, and things get worse. thats what my problem was.

so i advanced my timing (to around 0.7 degrees retard per psi) and as long as my a/f ratio is around 12.5:1 or leaner, i boost normally. if it retard my timing or add fuel, i get a boost spike and my WG may or may not be able to handle it.



one of the things you'll notice is that my boost level is wiggling a little before it gets too rich and creeps up. this is a normal "ringing" effect that i am going to try to get rid of with putting the WG on its own line and trying different sources for boost. the aem ems does have an algorithm to compensate for this ringing but i am not messing with that any time soon. just so happy i figured this **** out.

 

wow, just wow. Great investigation work. i did not know your timing was so rerarded.

 

Good work, Joe!

I was talking to a guy awhile back that did tuning on a lot of real
high end cars. He was telling me that he would set things up so
that during an upshift, the injectors would keep firing (no spark).
The "raw" gas would burn in the turbine housing and keep the turbo
spooled.

Your results seem to be similar to what he was talking about.

Sonny

 

on me for playing it too safe and thinking it wouldnt matter. at least i learned a lot. yeah thanks Sonny i was basically making my own anti-lag setup, except at full boost. haha.

 

Im glad you got it figured out joe. Now come help me..hehe

art

 

You ******* evil genius. I stand here in awe. Excellent work!

 

Yet again shows sometimes you just have to step back and look into how things work. I tuned a friends DSM about 3 weeks ago, and in order to decrease spool time before full boost we have the timing retarded and the fuel curve adjusted on the positive side. As soon as I got to this thread, I thought of the same thing for you, but you all got to it and thought it through before I could even post.

 

nice info !

 

cool, nice to see you finally figured that out. i think you had some of us internal wg people worried we would encounter this problem in the near future. so we can clear that greddy 3 in exhaust boost spike myth rite?

 

yup its in the tuning.

 

cool, i was worried about freeing up the exhaust.